Having suffered with a knee injury, the world number five pulled out of January's Australian Open with a stomach virus.

The Spaniard saved two break points on his opening service game and looked to be on course for victory after wrapping up the first set in a tie-break.

But Zeballos refused to buckle and took the second set after another tight tie-break.

Zeballos beat Nadal to win his first ATP Tour title

There had been no breaks of serve up to that point, but Nadal changed that by winning the opening game of the third set - only to relinquish his advantage immediately.

At 5-4 ahead, Zeballos made his move and charged into a 0-40 lead on Nadal's serve before converting his first match point and sealing victory after two hours and 46 minutes.

Nadal, though, was positive in defeat, despite missing out on his 37th clay-court title.

"It was a great tournament for me," he said. "I just need to keep working, practising with hope, motivation and the right attitude to have better sensations every week. I hope it's the beginning of a lot of good things for me."

There was more disappointment for the Spaniard after he and Argentina's Juan Monaco were later beaten in the doubles final, losing 6-2 6-4 to Italians Paolo Lorenzi and Potito Starace.